1. Field of the Invention
The present invention relates generally to the field of Liquid Crystal Display (LCD) devices, and more specifically to a method and system for improving technology for aligning the backplane (substrate) surface for enhancing alignment of the liquid crystal.
2. Description of the Prior Art
In past 20 years, liquid crystal display has grown in to multi billion dollar industry and products implementing LCD device can now be found in hand held devices, small size color televisions, laptop computers, and projection systems, and LCDs are increasingly being used for desktop computers.
One conventional LCD device includes liquid crystal cells having liquid crystal sandwiched between transparent electrodes formed on opposed glass substrates (i.e., plates) Another conventional LCD device includes liquid crystal cells having liquid crystal sandwiched between a transparent electrode on glass substrate and a reflective electrode on a non-transparent or transparent substrate (e.g., silicon). In either case, an electrical signal is selectively applied between the electrodes to allow the device to modulate incident light and display information. To obtain contrast, the orientation of the liquid crystal molecules must be uniformly controlled. In a field effect system such as a nematic system (which is designed to twist the liquid crystal molecules by about 0° degrees to 270° degree between the upper and lower plates), it is preferable to orient the liquid crystal molecules parallel to the substrate surface in a unidirectional manner. The liquid crystals can be aligned through stretching a polymer, rubbing a polymer, depositing a polymer in the form of a Langmuir Blodgett film, or exposing a polymer film to UV radiation. Additionally, alignment can be achieved by depositing SiOx on substrates or by etching grooves using microlithography.
One popular alignment technique is to deposit a polyimide alignment (PI) film on each transparent electrode to orient the liquid crystal, and then to rub or abrade the polyimide film in a desired direction. More specifically, a polyimide film is formed by applying a wet coat of polyimide solution to a substrate using known printing or spinning techniques. The wet coat is baked to form a polyimide film on the substrate. After the polyimide film is formed on the substrate, the molecular structure of the film must be aligned in a desired direction in order to orient the liquid crystal molecules in the desired direction. For this purpose, the polyimide film is rubbed in the desired direction with a gigged, flocked, or velvet cloth, and then cleaned to remove debris from the rubbing. In this manner, an alignment film is formed as an insulating layer with an atomic structure aligned so as to orient the liquid crystal molecules in the desired direction.
Rubbing the polyimide alignment film by cloth is still the standard method in multibillion dollar state of art fabrication facilities. However, this polyimide rubbing method produces debris, causes ESD damages, and requires after rubbing cleaning.
Non-rubbing alignment technology is now a hot research topic in the LCD industry as well as in universities. The present assignee International Business Machines Corporation (Armonk, N.Y.) has protected technology implementing low energy ion beam (IB) treatment of inorganic films such as diamond like carbon films to align liquid crystals. For instance, U.S. Pat. Nos. 6,195,146, 6,124,914, 6,346,975 and 6,577,365 each describe methods implementing ion beam bombardment of the alignment layers.
Comparing to the other non-rubbing alignment methods such as photo-treatment of organic thin films, the ion beam treatment on diamond-like film (DLC) or other inorganic thin films for the alignment of liquid crystals has the advantages of dry film deposition, non contact alignment process, short process time and reduced processing steps. The alignment by ion beam treatment on DLC film abbreviated as DLC IB alignment is more uniform and has less image-sticking than conventional rubbed-PI alignment. However, it is found that DLC alignment tends to have more disclinations, which is the defect where liquid crystal molecules tilt to different directions, associated with reverse twist domain than PI alignment. In addition, the azimuthal anchoring energy, which is the energy binding to liquid crystal molecules to certain orientation, of DLC alignment is weaker than PI alignment resulting in a deviation larger than ±1° in the twist angle. The deviation in the twist angle should be less than about ±1° for in-plane-switching (IPS) mode. Weak anchoring is also a potential problem for long term reliability. Further more, DLC alignment has a meta-stable alignment state that is perpendicular to the IB direction. Particularly, LC molecules tend to align perpendicular to the IB direction on such DLC surfaces. The meta-stable state is part of the reason for existence of reverse twist domains.
It would thus be highly desirable to provide a system and method implemented in LCD display manufacture that enhances the alignment of the liquid crystal material using diamond-like film (DLC) or other inorganic thin alignment layers.
While provision of grooves for liquid crystal (LC) alignment is one of the oldest liquid crystal alignment methods (See for example, U.S. Pat. Nos. 5,438,421, 6,466,296) usually it has a low anchoring energy and is difficult to produce which is why polyimide rubbing is the preferred industry standard.
It is believed that there has heretofore never been an LCD alignment technique that utilizes the provision of grooves in DLC or other inorganic thin alignment layers for enhancing the alignment of the liquid crystal material.